Air handling unit mixing method and system

ABSTRACT

A mixing chamber for an air handling unit having a first inlet, second inlet and an outlet. The first inlet receives a first air stream. The second inlet to receives a second air stream. The outlet discharges a mixed airflow. The first inlet includes a first damper having an opposed blade configuration for controlling the flow of the first air stream and the second inlet includes a second damper having an opposed blade configuration for controlling the flow of the second air stream. The mixing chamber also includes a control arrangement to control operation of the first and second damper. The control arrangement is configured to independently open and close each of the first and second dampers to regulate airflow into the mixing chamber.

FIELD OF THE INVENTION

The present invention is directed to an air handling unit for a heating, ventilation and air-conditioning (HVAC) system. In particular, the present invention is directed to a system and method for mixing air in variable air volume air handling systems.

BACKGROUND OF THE INVENTION

HVAC systems typically include an air handling unit. The air handling unit contains various components for conveying air from and into an indoor space. Among the components of the air handling unit is a mixing box. A mixing box is a component that mixes two or more streams of air in order to provide a mixed stream of air having a substantially uniform temperature and composition. Ineffective mixing of air streams may result in non-uniform heating or cooling of the conditioned space, and in some cases may cause damage to the system.

One type of air handling unit used commercially is a variable air volume system. A variable air volume system is a system that provides a variable volume of air at a substantially constant temperature. Typically, the return air (i.e., air brought from an indoor space) is mixed with outdoor air and then heated or cooled to provide air suitable for delivery back to the indoor space. The volume of air going to the indoor space is varied, as required, by the air handling unit. If more cooling or heating is required, the volume of air is increased to the space. If less cooling or heating is required, the volume of air is decreased to the space.

Variable air volume air handling systems typically utilize mixing chambers to provide some control of the air temperature. One type of mixing chamber mixes return air with outdoor air to produce air having a desired temperature. Mixing chambers used with variable air volume air handling systems generally have parallel blade damper systems that are modulated together to achieve mixing of air streams. One damper system is used to admit air from the return air stream to the mixing chamber and another damper system is used to admit outdoor air. The parallel blades of the dampers are configured to direct the streams of air toward each other, when positioned partially open, in order to effect mixing. Directing the streams toward each other has the drawback that much of the air in one stream passes through the second stream without adequate mixing. In order to overcome this drawback, an air blender is generally used to mix the combined stream. The use of an air blender results in more equipment and a larger pressure drop for the system. The larger pressure drop may require a larger fan and may require more fan energy, even when the system is operating with only one of the outdoor air or return air dampers being open.

Under most local building codes, variable volume air handling systems must bring in at least some outdoor air into ventilation systems during operation of the ventilation system. This is a particular problem when the outdoor temperature is excessively cold, is excessively warm, or when the outdoor air contains pollutants. If the outdoor air is sufficiently cold and mixing of the return air is insufficient, the cold air stratifies (i.e., separates) in the air handling system and freezes water in the heating or cooling coil. If pollutants are present in the air, such as days having high ozone levels, it is desirable to minimize the amount of outdoor air in order to minimize the amount of pollutant brought into the building, while maintaining sufficient air volume within the system as well as blending the air so that it is equally distributed to all spaces within the building. Current systems fail to provide sufficient control of the ratio of outside air to inside air and fail to provide sufficient mixing of the air passing over the heating or cooling coil to prevent freezing of the water in the coil and to minimize the concentration of pollutants present in the indoor space.

Therefore, what is needed is a method and system for sufficiently mixing streams of air in variable air volume air handling units and that can control the ratio of incoming air streams.

SUMMARY OF THE INVENTION

One embodiment of the present invention includes a mixing chamber for an air handling unit having a first inlet, second inlet and an outlet. The first inlet receives a first air stream. The second inlet to receives a second air stream. The outlet discharges a mixed airflow. The first inlet includes a first damper having an opposed blade configuration for controlling the flow of the first air stream and the second inlet includes a second damper having an opposed blade configuration for controlling the flow of the second air stream. The mixing chamber also includes a control arrangement to control operation of the first and second damper. The control arrangement is configured to independently open and close each of the first and second damper to regulate airflow into the mixing chamber.

Another embodiment of the present invention includes an air handling unit having a mixing chamber, an air moving device and a control device. The mixing chamber includes a first inlet, a second inlet and an outlet from the mixing chamber. The first inlet receives a first air stream. The second inlet to receives a second air stream. The outlet discharges a mixed airflow. The first inlet includes a first damper having an opposed blade configuration for controlling the flow of the first air stream and the second inlet includes a second damper having an opposed blade configuration for controlling the flow of the second air stream. The control device is configured to independently operate a corresponding damper to open and close the corresponding damper to regulate airflow into the mixing chamber.

Another embodiment of the present invention includes a method for mixing air in an air handling unit. The method includes providing a mixing chamber comprising having a first inlet, a second inlet and an outlet. The first inlet receives a first air stream. The second inlet receives a second air stream. The outlet discharges a mixed airflow. The first inlet includes a first damper having an opposed blade configuration for controlling the flow of the first air stream. The second inlet includes a second damper having an opposed blade configuration for controlling the flow of the second air stream. An air stream condition is sensed. In response to the condition sensed, each of the first damper and second damper are operated between an open position and a closed position to regulate airflow into the mixing space to provide a predetermined mix of airflow condition.

An advantage of the present invention is that the incoming air is mixed in the mixing chamber to produce air having a substantially uniform temperature and composition to pass over the heating or cooling coil.

Another advantage of the present invention is that mixing of the air occurs without the requirement of having an air blender, which increases the pressure drop and fan requirements for the air handling system.

Another advantage of the present invention is the mixing of the air streams with minimal pressure drop. The substantial lack of pressure drop reduces the fan operating costs by requiring either a smaller fan and/or less horsepower to circulate air.

Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically an air handling system, as known in the art.

FIG. 2 schematically illustrates a parallel blade damper arrangement, as known in the art.

FIG. 3 schematically illustrates another air handling system, as known in the art.

FIG. 4 schematically illustrates an air handling system according to one embodiment of the present invention.

FIG. 5 schematically illustrates an opposed blade damper arrangement according to one embodiment of the present invention.

FIGS. 6-8 schematically illustrate various positions of the blades of an opposed blade damper arrangement according to one embodiment of the present invention.

FIG. 9 schematically illustrates still another air handling system, as known in the art.

FIG. 10 schematically illustrates an air handling system according to another embodiment of the present invention.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically illustrates a known HVAC system air handling unit. The air handling unit includes a mixing space 100, which receives air from a first inlet 103 and a second inlet 105. First inlet 103 includes a first linked actuator 110, and a first parallel blade damper 120. Second inlet 105 includes a second linked actuator 130, and a second parallel blade damper 140. The first inlet air stream 150, which is preferably air brought from the outdoors, passes through first parallel blade damper 120 into the mixing space 100. The second inlet air stream 160, which is preferably return air brought from the indoor space, passes through second parallel blade damper 140 into mixing space 100. The first and second linked actuators 110 and 130 move the first and second parallel blade dampers 120 and 140 together from a single control signal. The linkage of the first and second linked actuators 110 and 130 may be a mechanical linkage or a single control signal provided to both first and second linked actuators 110 and 130. The control is provided such that the first parallel blade damper 120 opens as the second parallel blade damper 140 closes and the second parallel blade damper 140 opens as the first parallel blade damper 120 closes. The first and second inlet air streams 150 and 160 are drawn by blower 190 through the first and second parallel blade dampers 120 and 140 into the mixing space 100 and then through a filter 170 and across a heating or cooling coil 180. Heating or cooling coil 180 may contain a heat transfer fluid susceptible to freezing, such as steam or water. When the air stream passes over coil 180, heat is transferred to or from the first and second inlet air streams 150 and 160. If the air passing over the coil 180, or a portion thereof, is sufficiently cold, and the water or steam in the coil 180 is not moving with sufficient velocity in the coil 180, freezing of the medium, such as water or steam in the coil 180 can occur when the cold air comes into contact with the coil 180. This freezing of the heat transfer fluid in the coil 180 may result in damage or failure of the coil 180. When the first and second parallel blade dampers 120 and 140 are partially opened, the position of the blades provide air streams that flow toward each other. The air streams pass through each other after passing through the first and second parallel blade dampers 120 and 140 but are not sufficiently mixed, which insufficient mixing results in stratification of the air stream and the possible freezing of the coil, as discussed above, when the air drawn from the outside is sufficiently cold.

FIG. 2 schematically shows a parallel blade damper 210 known in the art. The parallel blade damper 210 includes parallel damper blades 220 that each rotate in the same direction 225 about a rotational axis, depending on the desired air flow through the parallel blade damper 210. The inlet airflow 230 enters the parallel blade damper 210 at an angle substantially perpendicular to the parallel damper centerline 235. The parallel damper centerline 235 runs through the rotational axis of each of the parallel damper blades 220. The outlet airflow 240 exits at an angle to the centerline approximately equal to the angle the parallel damper blades 220 with respect to parallel damper centerline 235. The outlet airflow 240 leaving the parallel blade damper 210 retains a substantially laminar flow profile. The outlet airflow 240 does not mix when contacted with other streams of air. The laminar flow profile does not promote mixing and results in the streams of air passing through each other with little or no mixing of the air or heat transfer between the air streams

FIG. 3 shows another known system having approximately the same arrangement of mixing space 100, first and second linked actuators 110 and 130, first and second parallel blade dampers 120 and 140, first and second inlet air streams 150 and 160, filter 170, heating or cooling coil 180 and blower 190, as shown in FIG. 1. As in FIG. 1, the first and second parallel blade dampers 120 and 140 operate together to provide airflow streams that are directed toward each other. Like in FIG. 1, the first parallel blade damper 120 closes as the second parallel blade damper 140 opens and the second parallel blade damper 140 opens as the first parallel blade damper 120 closes. FIG. 3 further includes an air blender 310 in the mixing space 100 to facilitate mixing of the first and second inlet air streams 150 and 160. The air blender 310 is placed in the system to overcome the problem of insufficient mixing discussed above with respect to FIGS. 1 and 2. The air blender 310 is additional equipment that takes up space in the system and causes an additional pressure drop, which increases the requirements for the blower 190 to move air through the system. In addition, even when no mixing is required, as when the first or second parallel blade damper 120 or 140 is fully open and the other damper is closed, a pressure drop is still present due to the air blender 310.

FIG. 4 schematically shows one embodiment of the present invention. FIG. 4 shows an air handling unit including a mixing space 100, a first inlet 103, a second inlet 105, a filter 170, a heating or cooling coil 180 and a blower 190, whose components are present substantially as shown and described with respect to FIG. 1. However, FIG. 4 further includes a first independent actuator 410 that controls a first opposed blade damper 420 positioned within the first inlet 103. FIG. 4 also includes a second independent actuator 430 that controls a second opposed blade damper 440 positioned within the second inlet 105. The first and second opposed blade dampers 420 and 440 are dampers having blades that rotate adjacent blades in opposite directions. Although FIG. 4 has been shown with a first and second inlet 103 and 105, any number of inlets may be present, including three or more inlets, so long as the inlets each include an opposed blade damper arrangement.

This embodiment of the invention includes a sequencing of the first and second opposed blade dampers 420 and 440. The independent actuators permit positioning of the opposed blades 520 (see FIG. 5) in the first and second opposed blade dampers 420 and 440 to any position from fully open to fully closed. Although FIG. 4 has been described with respect to a first and second independent actuator 410 and 430, the opposed blades 520 of the first and second opposed blade dampers 420 and 440 may be positioned by any suitable device that provides independent positioning of each of the first and second opposed blade dampers 420 and 440. The first and second independent actuators 410 and 430 are controlled by a controller 450. The controller 450 may be any suitable control device, so long as the control device is capable of providing the appropriate control signals to each of the first and second independent actuators 410 and 430 to independently position the opposed blade dampers 510. While shown as separate controller 450 and first and second independent actuators 410 and 430, the control device may include the mechanisms of the first and second independent actuators 410 and 430 and may be controlled independently as a control device for the first opposed blade damper 420 and the second opposed blade damper 440.

Controller 450 may receive inputs from one or more sensors (not shown), including, but not limited to, temperature, carbon dioxide concentration, carbon monoxide concentration, particulate concentration, pollution concentration and/or humidity measuring devices. The sensor for input to the controller 450 may be placed in any suitable location to sense conditions desired for control of the first and second opposed blade dampers 420 and 440. For example, when controlling the heating and/or cooling load, temperature sensors may be utilized to sense the temperature of the outdoor air and the temperature of the recirculated indoor air. Controller 450 determines the blade position for each of the first and second opposed blade dampers 420 and 440 based upon the cooling, heating and/or outdoor air ratio requirements of the system. In addition, the controller may determine blade positions for each of the first and second opposed blade dampers 420 and 440 based upon the presence or absence of pollution or other contaminates in the air. For example, the first opposed blade damper 420 may be placed in a closed position and the second opposed blade damper 440 may be placed in an open position in response to undesirable conditions, such as the presence of pollution, particulates or carbon monoxide, in the first inlet air stream 150. Likewise, the first opposed blade damper 420 may be placed in an open position and the second opposed blade damper 440 may be placed in a closed position in response to desirable conditions, such as desired temperature, humidity or low pollution, sensed in the first inlet air stream 150.

Sequencing of the first and second opposed blade dampers 420 and 440 is achieved by controlling the first and second opposed blade dampers 420 and 440 independently. The positioning of the first and second opposed blade dampers 420 and 440 is related to the desired air temperature and the amount of mixing required. In one example related to fan start-up, the first opposed blade damper 420 is in the closed position, wherein flow of first inlet air stream 150, preferably outdoor air, is blocked and the second opposed blade damper 440 is opened to allow the maximum flow of air through the second inlet 105, preferably return air. Next, the first opposed blade damper 420 is modulated open in order to provide mixing of the air in the mixing space 100, while the second opposed blade damper 440 remains fully open. The position of the first opposed blade damper 420 is such that a predetermined temperature of the air mixture is maintained.

In another example, the controller 450 may receive a signal from a sensor, such as a carbon dioxide sensor, that indicates that a large ventilation load is required in a particular indoor space. The first and second opposed blade dampers 420 and 440 may then each be positioned to provide additional or increased airflow. Specifically, the first opposed blade damper 420 may be opened to provide a greater airflow and the second opposed blade damper 440 may be opened to provide a greater airflow. In addition, the controller 450 may sense an increased level of outdoor pollution, wherein the first and second opposed dampers 420 and 440 may be controlled sequentially to increase the amount of return air and decrease the amount of outdoor air, thereby controlling the ratio of outdoor air.

In still another example, the controller 450 may sense that the air temperature upstream of the coil 180 is greater or less than a desired temperature. For example, the desired temperature may be about 50-60° F. (10-16° C.), depending on the requirements of the building. If the outdoor temperature is cooler and the temperature of air passing over the coil 180 is higher than the desired temperature, the opposed damper for the outdoor air may be positioned to permit more cold air into the mixing space 100, while maintaining the position of the second opposed blade damper 440 admitting the return air. If the outdoor temperature is warmer and the temperature of the air passing over the coil 180 is higher than the desired temperature, (typically greater than 75° F. (24° C.) the first opposed blade damper 420 for the outdoor air may be positioned to permit less warm air into the mixing space 100 to reduce the load on the cooling coil 180.

FIG. 5 schematically illustrates an opposed blade damper 510 for use in the system of the present invention. The opposed blade damper 510 includes a plurality of opposed blades 520 that are arranged so that adjacent opposed blades 520 rotate in opposite directions about a rotational axis. The opposed blade damper 510 shown in FIG. 5 is suitable for use in the present invention. In one embodiment, opposed blade damper 510 is used as both the first and second opposed blade dampers 420 and 440 as shown in FIG. 4. The opposed blade damper 510 provides good mixing when positioned in a partially open position because the air leaving the opposed blade damper 510 has a substantially turbulent flow profile. The turbulent flow is due to the dead space 540 of lower air pressure being adjacent to jet space 550 of higher air pressure on the outlet side of the opposed blade damper 510. Air from the jet space 550 at least partially circulates to the dead space 540 and results in at least partially turbulent flow. The turbulent flow and separated jet profile provides increased mixing within the mixing space 100 and allows two or more airstreams to be sufficiently mixed in the mixing space 100 to provide a combined stream substantially free of stratified (i.e., separated) air and having substantially uniform temperature and properties. The geometry of opposed blades 520 may be any suitable geometry that produces the turbulent flow profile.

FIGS. 6-8 schematically illustrates the operation of an opposed blade damper 510 for use in the system of the present invention. FIG. 6 shows an opposed blade damper 510 in the closed position. Directional arrows 610 illustrate the operation of the opposed blades 520 when the opposed blades 520 are moved from a closed position to a partially open position.

FIG. 7 shows the opposed blade damper 510 in a partially open position. The opposed blades 520 continue to rotate in the direction of the directional arrows 610. The position shown in FIG. 7 permits flow of air that is greater than the closed position (see FIG. 6) and less than the open position (See FIG. 8). The air flow traveling through the opposed blade damper 510 exits the opposed blade damper 510 in a manner that results in increased mixing within the mixing space 100. The partially open position shown in FIG. 7 provides the turbulent flow profile that increases the mixing of the air.

FIG. 8 shows the opposed blade damper 510 in a fully open position. The opposed blades 520 are positioned perpendicular to the centerline 530. The position of the opposed blades 520 permits the maximum flow of air through the opposed blade damper 510.

The operational positioning shown in FIGS. 6-8 provides the range of modulation used in sequencing the dampers. The dampers have independent controls and can be independently positioned in order to provide the desired ratio of air from the various air streams. The opposed blades 520 may be configured into any position from the closed position shown in FIG. 6 to the open position shown in FIG. 8. Positioning each of the dampers independently and sequentially permits the air handling unit to operate with a minimal pressure drop while providing a variable ratio of air from the various inlet air streams. Variable ratios of outdoor air, for example, may provide reduction in pollution levels.

FIG. 9 shows an alternate view of an air handling unit in the known art. FIG. 9 includes mixing space 100, first and second linked actuators 110 and 130, first and second parallel blade dampers 120 and 140, first and second inlet air streams 150 and 160, filter 170, heating or cooling coil 180 and blower 190, substantially as described above and shown in FIG. 1. FIG. 9 further includes a first and second outlet 905 and 907. The first and second outlets 905 and 907 supply air to various indoor spaces. First and second inlet air streams 150 and 160 fail to sufficiently mix and stratify in the mixing space 100. The stratification of the first and second inlet air streams 150 and 160 resulting from insufficient mixing causes a first outlet airstream 910 to contain primarily return air and little if any outdoor air. Likewise, a second outlet airstream 920 contains primarily outdoor air and little if any return air. The lack of sufficient mixing results in indoor spaces having an uneven heating or cooling or uneven ventilation air.

FIG. 10 shows an alternate view of an air handling unit according to another embodiment of the present invention. FIG. 10 includes a mixing space 100, a first inlet 103, a second inlet 105, a filter 170, a heating or cooling coil 180 and a blower 190, whose components are present substantially as shown and described with respect to FIGS. 1 and 9. FIG. 10 further includes first independent actuator 410, first opposed blade damper 420, second independent actuator 430, and second opposed blade damper 440, as shown and described with respect to FIG. 4. The first inlet air stream 150 passes through first opposed blade damper 420 and enters the mixing space having at least a partially turbulent flow profile. The air entering mixing space 100 from first opposed blade damper 420 converges with the air passing over the second opposed blade damper 440 from second inlet air stream 160. In this embodiment, the second opposed blade damper 440 is positioned in a fully open position. The converging first and second inlet air stream 150 and 160 mix to produce an airstream having substantially uniform temperature and properties. The mixed airstream provides a first and second outlet 910 and 920 providing substantially uniform heating or cooling to each of the indoor spaces.

The variability of each of the first and second opposed blade dampers 420 and 440 provides a method in which the temperature of the air may be controlled, while simultaneously providing a method in which the ratio of indoor air to outdoor air may be varied. Controller 450 senses the appropriate inputs and independently determines the position of the first and second opposed blade dampers 420 and 440 based upon the cooling, heating and/or outdoor air ratio requirements of the system. To control the temperature within the variable air volume system, temperature sensors measuring the temperature of the air upstream of the coil 180 and outdoor temperature sensors may be used. A higher outdoor temperature that is still below the desired mixed air temperature may cause the controller to open the first opposed blade damper 420, while the second opposed blade damper 440 remains in an open position, to permit a larger volume of air from the outdoors to enter the system when the temperature of the air passing over the coil 180 is above the desired temperature. Likewise, the first opposed blade damper 420 may be closed, while the second opposed blade damper 440 remains in a stationary position, to permit a smaller volume of air from the outdoors to enter the system when the temperature of the air passing over the coil 180 is below the desired temperature. To control the ratio of outdoor to indoor air, the dampers may be individually, but sequentially, controlled on the basis of temperature, humidity or pollutants present in the return air or outdoor air. Sensors measuring pollutant levels may be used to determine whether return air or outdoor air contains an undesirable level of pollutants. In the example where pollution is present in the outdoor air, the first opposed blade damper 420 may be closed to provide a smaller amount of outdoor air flow into the system, while the second opposed blade damper 440 remains in a stationary position, resulting in a larger ratio of return air to outdoor air. Likewise, if the return air contains an undesirable amount of pollutants, the first opposed blade damper 420 may be opened to provide a larger amount of air flow into the system, while the second opposed blade damper 440 closes or reduces the flow of return air, resulting in a larger ratio of outdoor air to return air.

The first and second independent actuators 410 and 430 permit the first and second opposed blade dampers 420 and 440 to independently be positioned at any angle with respect to the inlet air stream 150 and 160. Controller 450 provides the desired return air to outdoor air ratio and uniform temperature by opening and closing the first and second opposed blade dampers 420 and 440 sequentially. In one example, second opposed blade damper 440 is open and first opposed blade damper 420 is closed. With this arrangement, the airstream leaving the mixing space 100 is about 100% return air. In order to provide the desired return air to outdoor air ratio and uniform temperature, controller 450 sequentially modulates first opposed blade damper 420 to a fully open position, while second opposed blade damper 440 remains fully open. With this arrangement, the leaving airstream is about 50% outdoor air. Controller 450 may also modulate second opposed blade damper 440 closed until the airstream leaving the mixing space 100 is about 100% outdoor air.

In another example, the first and second opposed blade dampers 420 and 440 are positioned fully open to provide about 50% outdoor air. This arrangement of damper position permits the supply of about 50% outdoor air with approximately 25% of the pressure drop that occurs in the linked parallel blade arrangement shown in FIGS. 1, 3 and 9 if both dampers are positioned to provide about 50% outdoor air.

The use of an opposed blade damper arrangement in conjunction with the independent positioning of each of the first and second opposed blade dampers 420 and 440 results in reduced horsepower requirements for the fan. For example, for a fully open position inlet air velocity through one of the first or second opposed blade dampers 420 and 440 may be 1100 fpm with a pressure drop of about 0.4 inch of water gauge (in. w.g.). The first and second opposed blade dampers 420 and 440 in a 50% closed position results in a pressure drop of about 1.75 in. w.g. The first and second opposed blade dampers 420 and 440 both opened in a fully open position results in air velocity through each damper of about 550 fpm with a pressure drop of about 0.10 in. w.g. The independent opening of the opposed blade arrangement, when 50% outdoor air is desired, results in a saving in pressure drop of 1.65 in. w.g. This savings in pressure drop with a 4 in. w.g. total static pressure system results in a required fan horsepower of only 45% of the horsepower required for systems that have dampers that operate by linked modulation. In a fan system having a 25 horsepower fan having a 30,000 CFM airflow capacity, the horsepower requirements for producing a 50% outdoor air airflow requires about 11.25 horsepower by using independent sequencing of the first and second opposed blade dampers 420 and 440, compared to a linked damper system, which requires a substantially maximum horsepower, e.g., up to about 25 horsepower in the above example, to provide 50% outdoor air airflow.

Additionally, with the first and second opposed blade dampers 420 and 440 fully open, the airstream is sufficiently mixed to provide substantially uniform air temperatures and properties. When the first and second inlet air stream 150 and 160 pass through the fully open damper, the air velocity is sufficiently low that the air does not experience stratification. Lower velocity air is permitted to circulate in the mixing space and provide sufficient mixing to prevent stratification of the air and freezing of the coil 180.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A mixing chamber for an air handling unit, the mixing chamber comprising: a first inlet to receive a first air stream; a second inlet to receive a second air stream; an outlet to discharge a mixed airflow; the first inlet comprising a first damper having an opposed blade configuration for controlling the flow of the first air stream; the second inlet comprising a second damper having an opposed blade configuration for controlling the flow of the second air stream; and a control arrangement to control operation of the first and second damper, the control arrangement being configured to independently open and close each of the first and second damper to regulate airflow into the mixing chamber.
 2. The mixing chamber of claim 1, wherein the first air stream comprises outdoor air.
 3. The mixing chamber of claim 1, wherein the second air stream comprises indoor air.
 4. The mixing chamber of claim 1, wherein the mixed airflow has a substantially uniform temperature.
 5. The mixing chamber of claim 1, wherein the control arrangement further includes a sensor to sense a condition selected from the group consisting of temperature, humidity, carbon dioxide concentration, carbon dioxide concentration, pollution concentration and combinations thereof.
 6. The mixing chamber of claim 5, wherein the condition is sensed in one or both the first air stream and the second air stream and the control arrangement is configured to open or close one or both of the first and second dampers in response to the sensed condition.
 7. The mixing chamber of claim 6, wherein the control device is configured to position the first damper and the second damper to obtain a predetermined mix of airflow condition.
 8. An air handling unit comprising: a mixing chamber comprising a first inlet to receive a first air stream; a second inlet to receive a second air stream; an outlet to discharge a mixed airflow; the first inlet comprising a first damper having an opposed blade configuration for controlling the flow of the first air stream; the second inlet comprising a second damper having an opposed blade configuration for controlling the flow of the second air stream; an air moving device; and a control device configured to independently operate each of the first and second damper to open and close each of the first and second damper to regulate airflow into the mixing chamber.
 9. The air handling unit of claim 8, wherein the first air stream comprises outdoor air.
 10. The air handling unit of claim 8, wherein the second air stream comprises indoor air.
 11. The air handling unit of claim 8, wherein the mixed airflow has a substantially uniform temperature.
 12. The air handling unit of claim 8, wherein the control device further includes a sensor to sense a condition selected from the group consisting of temperature, humidity, carbon dioxide concentration, carbon dioxide concentration, pollution concentration and combinations thereof.
 13. The air handling unit of claim 12, wherein the condition is sensed in one or both the first air stream and the second air stream and the control device is configured to open or close one or both of the first and second dampers in response to the sensed condition.
 14. The air handling unit of claim 13, wherein the control device is configured to position the first damper and the second damper to obtain a predetermined mix of airflow condition.
 15. A method for mixing air in an air handling unit comprising: providing a mixing chamber comprising a first inlet to receive a first air stream; a second inlet to receive a second air stream; an outlet to discharge a mixed airflow; the first inlet comprising a first damper having an opposed blade configuration for controlling the flow of the first air stream; the second inlet comprising a second damper having an opposed blade configuration for controlling the flow of the second air stream; sensing an air stream condition; and operating each of the first damper and second damper between an open position and a closed position to regulate airflow into the mixing space to provide a predetermined mix of airflow condition in response to the sensed condition.
 16. The method of claim 15, wherein the first air stream comprises outdoor air.
 17. The method of claim 15, wherein the second air stream comprises indoor air.
 18. The method of claim 15, wherein the mixed airflow has a substantially uniform temperature.
 19. The method of claim 15, wherein the air stream condition sensed is a condition selected from the group consisting of temperature, humidity, carbon dioxide concentration, carbon dioxide concentration, particulate concentration, pollution concentration and combinations thereof.
 20. The method of claim 19, wherein the condition is a condition of one or both the first air stream and the second air stream.
 21. The method of claim 20, wherein the first damper in positioned into a closed position and the second damper is positioned into an open position in response to an undesirable condition sensed in the first air stream.
 22. The method of claim 21, wherein the first damper is positioned into a closed position and the second damper is positioned into an open position in response to an desirable condition sensed in the first air stream. 